Retinal photoreceptors in albino rats undergo rapid degeneration after exposure to low-intensity visible light. Exposure to more intense illumination is necessary for receptor damage in pigmented rats and other species such as the monkey. Photoreceptors are less damanged by light exposure in ovariectomized and hypophysectomized animals, and prolactin administration reverses the protection afforded by hypophysectomy. Proposed projects will examine further the role of prolactin and gonadal hormones on retinal degeneration. Adrenal-gonadal and pituitary gland-adrenal relationships will be studied in gonadectomized and hypophysectomized animlas supplemented with pituitary and target cell hormones. Autoradiographic experiments are designed to determine the minimal intensity and duration of light exposure to induce a phagocytic response to retinal injury. The influence of biogenic amines on endogenous estrogen and prolactin levels and on photoreceptor damage will be evaluated. The "normal" and experimentally modified endocrine status of rats with hereditary retinal dystrophy will be investigated in relation to light-induced retinal damage. Methodologic approaches will include not only surgical manipulations, but the administration of pharmacologic agents known to influence serum hormone levels, and the localization and concentration of hormones in retinal tissue using autoradiography and liquid scintillation spectroscopy.